X1024 Sensor Chip Assemblies Scas

Hybridization of 1024*1024 Si:As IBC detector arrays to MIRI readouts has resulted in several excellent SCAs. With 25 ^m pixels, the detecting area is approximately 1 inch by 1 inch. Nearly all SCAs fabricated to date have >99.5% of the 1048576 indium bumps making electrical contact between the detector and ROIC and no degradation has been observed with repeated thermal cycling.

NASA Ames Research Center has made several key measurements of the MIRI SCAs. Figure 3 shows dark current spatial uniformity of a 1024*1024 SCA and an Arrhenius plot of log(dark current) as a function of 1000/Temperature as measured by NASA Ames. The dark current follows the expected straight line on the Arrhenius plot to 8K, indicating a thermally-

generated current. The dark current bottoms out at 0.2 e-/sec and appears to be uniform. The uniformity may be too good to be limited by the detector array and thus due to other effects such as dewar light leaks or hot spots. Since the detectors are sensitive to 28 ^m, areas inside the dewar slightly above 10 K can contribute to the measured "dark" current. Therefore, 0.2 e-/sec at 7 K may be an upper limit on the detector dark current.

Figure 2. Noise as a function of number of Fowler samples for an "alternate" MIRI ROIC.

Smooth curve represents expected 1/sqrt(N) noise reduction. While the majority of the data follow the curve, several points are above the line due to cosmic rays and excess noise in the first 80 rows.

Figure 2. Noise as a function of number of Fowler samples for an "alternate" MIRI ROIC.

Smooth curve represents expected 1/sqrt(N) noise reduction. While the majority of the data follow the curve, several points are above the line due to cosmic rays and excess noise in the first 80 rows.

Figure 3. Preliminary dark current measurement on SCA985 by NASA Ames. (left) The spatial plot shows the uniformity of the dark current over the 1024^1024 array. (right) An Arrhenius plot of log(dark current) vs. 1000/Temperature. The dark current decreases along a straight line on this plot down to approximately 8 K, as expected for a thermally generated current. An upper limit of 0.2 e-/sec was measured at approximately 4.8 K.

The response uniformity of the same SCA, SCA985, was also measured by NASA Ames. Figure 4 shows spatial response uniformity and relative response as a function of detector bias. Although these data are preliminary, the SCA appears to perform well.

Figure 4. Preliminary response measurement of SCA 985 by NASA Ames. (left) The spatial plot shows the uniformity of the response to infrared radiation over the 1024^1024 array. (right) The relative response as a function of detector bias. All measurements were made at 7 K.

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